1. Field of Application
The present invention relates to a rotor of an internal permanent magnet (hereinafter abbreviated to IPM) type of rotary electric machine, and in particular to a rotor of an IPM rotary electric machine in which magnetic flux barriers are disposed circumferentially adjacent to each of respective permanent magnets that are implanted within the rotor, for blocking a flow of magnetic flux from each permanent magnet.
2. Description of Prior Art
IPM rotary electric machines are well known in the prior art, with such a rotary electric machine having a plurality of permanent magnets implanted within the rotor rather than being mounted at the rotor surface. Such a type of rotary electric machine has various advantages over machines in which permanent magnets are mounted at the rotor surface, such as increased rotor strength and resistance to the effects of centrifugal force on the rotor. In addition, (when the rotary electric machine is operated as a motor) the motive torque that is developed by the rotor is made up of not only magnetic torque resulting from the flow of magnetic flux of the permanent magnets of the rotor, but also of reluctance torque that results from differences in magnetic resistance between respective circumferential portions of the rotor.
An example of a rotor for a prior art IPM rotary electric machine has been proposed in Japanese patent publication number 2000-60038 (referred to in the following as reference document 1). With that IPM rotary electric machine, two permanent magnets are utilized to constitute one pole of the rotary electric machine. The two permanent magnets are configured in a V-shape, which opens towards the outer circumferential periphery of the rotor. With such a configuration, the q-axis (quadrature axis) inductance (Lq) of the rotor is greater than its d-axis (direct axis) inductance (Ld) and as a result, the angular position of the rotor can be accurately detected based on variations in inductance.
Another example of a rotor for a prior art IPM rotary electric machine has been proposed in Japanese patent publication number 2001-339922 (referred to in the following as reference document 2). With that IPM rotary electric machine, permanent magnets are disposed in the rotor in the same manner as described in reference document 1. However in addition, a magnetic flux barrier (referred to in the following simply as a flux barrier) is disposed between each pair of permanent magnets, to thereby increase the reluctance torque.
Another example of a rotor for a prior art IPM rotary electric machine has been proposed in Japanese patent publication number 2002-44920 (referred to in the following as reference document 3). With that IPM rotary electric machine, which operates as a synchronous reluctance motor (i.e., a type of motor which does not normally incorporate permanent magnets, in the prior art) implanted permanent magnets are enclosed by flux barriers, to thereby provide a synchronous AC motor that utilizes both reluctance torque and magnetic torque.
Another example of a rotor for a prior art IPM rotary electric machine has been proposed in Japanese patent publication number 2003-324875 (referred to in the following as reference document 4). That IPM rotary electric machine is a motor that utilizes reluctance torque, wherein noise and vibration produced by the motor are reduced by employing specially shaped flux barriers.
Such prior art types of IPM rotary electric machine utilize permanent magnets that are formed of expensive materials such as rare earths, thereby increasing the manufacturing costs of such machines. It would be preferable to increase the level of reluctance torque that is developed in such a rotary electric machine, so that less expensive permanent magnets (i.e., producing lower levels of magnetic flux) could be utilized to thereby reduce the manufacturing cost, while maintaining a sufficiently high level of total torque that is a combination of the reluctance torque and magnetic torque.
In addition, such prior art types of IPM rotary electric machine have various disadvantages, as described in the following In the case of the rotary electric machines proposed in reference documents 1 and 2, two permanent magnets are utilized to form each pole of the rotary electric machine, so that the manufacturing operations to produce the rotor of such a machine are complex, and the total cost of the permanent magnets used in each machine is increased by comparison with that of a usual type of IPM rotary electric machine.
In the case of the rotary electric machine proposed in reference document 3, the torque is increased by comparison with a usual synchronous reluctance motor. However due to the fact that priority is given to increasing the flow of the q-axis magnetic flux, the shape of each permanent magnet (and hence, the shape of each of the magnet accommodation cavities within which the permanent magnets are respectively implanted) is determined by the shapes of the flux barriers, so that it is not possible to achieve a sufficient degree of magnetic torque.
In the case of the rotary electric machine proposed in reference document 4, in which the flux barriers are configured such as to reduce the level of vibration and noise produced by the rotary electric machine, no description is provided of a flux barrier configuration which would enable an increase in the output power produced by the rotary electric machine.
It would be highly advantageous to be able to increase the level of output power produced by an IPM rotary electric machine (i.e., level of electrical power output in the case of an electrical generator, or level of output shaft power, in the case of a motor), without increasing the size of the rotor, without increasing the number or size of permanent magnets that are installed in the rotor, and without increasing the manufacturing cost. However these advantages cannot be provided by prior art types of IPM rotary electric machine such as those described above. In particular, these prior art proposals do not describe any simple way (e.g., by altering the shape of the rotor) of increasing the level of output power at which output power saturation begins to occur, when an IPM rotary electric machine is operating at a high speed of rotation.
One factor which reduces the level of output torque or output power that can be obtained with a prior art type of IPM rotary electric machine is illustrated in FIG. 15, described in greater detail hereinafter. With such a prior art configuration, when q-axis magnetic flux passes from the stator into the rotor and flows between circumferentially adjacent flux barriers and then along a circumferential path below an implanted permanent magnet 12, a part of the q-axis magnetic flux will flow through a region closely adjacent to the radially inward face of the permanent magnet 12, i.e., after passing through the region indicated by the circle 2. As a result, some of the q-axis magnetic flux will be diverted, to flow into the permanent magnet 12, and this results in decreases in the level of available torque or output power, and a more rapid onset of output saturation, as the torque or output power level is increased.